Metal-oxide semiconductor (MOS) transistors generally include a substrate made of a semiconductor material, such as silicon. The transistors also include a source region, a channel region and a drain region within the substrate. The channel region is located between the source and the drain regions. A gate stack, which includes a conductive material gate or gate conductor on top of a gate oxide layer and sidewall spacers, is provided above the channel region. More particularly, the gate oxide layer is provided on the substrate over the channel region, while the gate conductor is provided above the gate oxide layer. The sidewall spacers help define locations of source and drain ion implantation and form self-aligned silicide.
The amount of current flowing through a channel of a semiconductor device is proportional to the mobility of the carriers in the channel. Thus, the operation speed of the transistor can be increased by increasing the mobility of the carriers in the channel. However, to obtain high performance of a MOSFET, it is necessary to scale down the channel length of the MOSFET. That is, the shorter the gate length results in a higher performance MOSFET. But, a shorter gate length requires a higher concentration of halo profile, which degrades carrier mobility or device performance.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.